PSI - Issue 24

Lorenzo Berzi et al. / Procedia Structural Integrity 24 (2019) 408–422 Berzi et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Looking at the interior, the vehicle has 8 seats and can transport further 20 standing passengers; 4 main vertical stanchions are installed on the pavement to be used for the passengers. Main aim of the retrofit in respect of vehicle layout have been: • to preserve the passenger compartment for demonstration use o the consequence is that large parts (converters, batteries and supercapacitors) have to be installed in the existing battery compartments • to support the pantograph without stressing the glassfiber bodywork o the consequence is that an additional frame anchored to the main steel frame has to be adopted and integrated with the interiors in order to not interfere with passengers • to maintain as much as possible the existing powertrain system for cost and reliability reasons o the consequence has been that lead batteries, power converters and control systems have been maintained.

Fig. 1. Structure of the vehicle adopted for the retrofit. Left: full glassfiber bodywork and steel frame subdivision. Right: Moving boxes for lead battery installation and swap demonstration

2.1. Layout of the electrical system

In order to let the flash recharge occur, two corresponding systems have to be installed in the transport system comprehending vehicle and infrastructure. The systems have been designed in order to provide in working condition up to 300 Wh/charge, that is significant for the size of the bus adopted since it can cover the energy consumption for approximately 0.5km. Scaling up is possible to support larger vehicles, the consumption being approximately 2kWh/km for a heavy 12m bus. Regarding the infrastructure, as described in literature (Ortenzi et al., 2018, 2019), the core of the system is constituted by an energy storage comprehending a stack of supercapacitors modules. The features can be synthetized as follows: • the power source for the infrastructure energy storage is a modular multilevel converter connected to the grid; the total power of the system is 8kW. • six supercapacitor modules – each one being composed by a bank of series-parallel units in order to achieve a nominal capacity of 63F and 125V as maximum – are installed on the infrastructure, and their layout as series elements can be modified using a group of contactors. • once that the vehicle is connected to the infrastructure using a pantograph – contact bars dome interface, the system closes the contactors accordingly to the effective status of energy storage on the vehicle. Then, current flows to the supercapacitor banks on the vehicle using an inductor as power limiting device. The